Electrochemical oxygen sensors traditionally comprise a gas diffusion working electrode, often based on a graphite/platinum catalyst dispersed on PTFE tape. Oxygen is reduced at this cathode while a balancing oxidation reaction takes place at a consumable anode (e.g., made of lead (Pb). The electrodes are held within an outer housing which contains a liquid electrolyte capable of supporting the relevant reactions, such as aqueous potassium acetate. The gas under test typically enters the housing through a controlled diffusion access port which regulates the ingress of oxygen into the cell. As the oxygen is reacted at the cathode, the electrical output of the sensor may be directly related to the ambient oxygen concentration. Such principles are well known and have been described.
Electrochemical gas sensors have a finite lifetime which depends on a number of factors. For oxygen sensors, the primary factor is the consumption of electrode material (e.g. a consumable lead counter electrode). Most types of sensors can also suffer from a gradual loss of activity of one or both electrodes, caused by the water drying out of the electrolyte. Clearly it is desirable for the sensor's working lifetime to be as long as possible but moreover it is important that any particular sensor type will consistently continue to work for at least the indicated lifetime. Early failures lead to the need for more frequent sensor replacement, as well as increased checking and monitoring of sensor performance and, ultimately, a loss in confidence in the sensor. Accordingly, there is a need to produce sensors that are more stable under many different operating environments.